Effect of B2O3 Concentration and Sintering Temperature on Microstructure and Electrical Properties in the ZnO-Bi2O3-Based Varistors
The ZnO-Bi2O3-MnO2-Co2O3-based (ZBMCO) varistors were prepared via the sol–gel method. The effects of B2O3 additive on the phase composition, microstructure, sintering temperature and electrical properties of the ZBMCO ceramics were studied. A single hexagonal ZnO phase was detected in all ZBMCO-xB2O3 varistors sintered at high temperature (1100°C). Secondary phases Mn0.31Bi1.69O2.85, Zn3B2O6, Bi24B2O39 and Bi2O3 were detected in ZBMCO-1.0 wt.%B2O3 varistors at a lower sintering temperature (900°C, 1000°C). The average grain size increased remarkably in the range of 15.27–26.12 μm with an increase of the B2O3 content. The ZBMCO-1.0 wt.%B2O3 varistor showed the maximum relative density of 97.2% with high nonlinear coefficient (56.5) and low leakage current (0.07 μA/cm2) at 1100°C. The E1mA decreased noticeably from 865 V/mm to 64 V/mm with an increase of the sintering temperature. When the sintering temperature is lower at 1000°C, the varistor exhibits relatively good electrical properties (α = 48.7, IL = 0.68 μA/cm2). These results demonstrate that low melting point B2O3 plays multiple roles in grain growth and microstructure.
KeywordsSol–gel route ceramics varistors sintering electrical performance
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